Reasoning GP · Algorithm · 1-page summary
Weight gain in adults
For: adults with new or progressive weight gain, face to face or remote. Not for: children (paediatric pathways) or long-term obesity care once causes are excluded (use the obesity protocol).
Core rule: decide fat or fluid first. Rapid gain with oedema, ascites or breathlessness is heart, kidney, liver or cancer until shown otherwise. Check TSH; test for Cushing's only with discriminatory features.
0Stop — call 999 now — before any history
- Weight gain with oedema and breathlessness at rest (acute heart failure, pulmonary oedema) → 999
- Severe bradycardia, cold, periorbital oedema and reduced consciousness (myxoedema coma) → 999 / A&E
- Acute kidney injury, severe electrolyte disturbance or decompensated liver disease → 999 / Same-day hospital
- Do not start empirical high-dose diuretics in primary care without an established diagnosis and a monitoring plan.
1Triage — fat or fluid? — check previous weights
| Pattern | Action |
|---|---|
| Cardiac | Oedema, orthopnoea, PND, raised JVP → NT-proBNP + ECG. >2000 ng/L → specialist + echo ≤2 weeks; 400–2000 → ≤6 weeks |
| Renal | Generalised oedema, frothy urine → ACR/PCR, albumin, U&E → Urgent nephrology discussion; Same-day if severe oedema, AKI, thrombosis, infection or unstable |
| Ascites / mass | Ascites or pelvic/abdominal mass in a woman → Gynae suspected cancer pathway without waiting for CA125. Any ascites → urgent USS, LFTs, albumin |
| Fat | Gradual, no oedema → blocks 2–5 |
2Screen — causes not to miss
- Cushing's: wide violaceous striae, proximal weakness, easy bruising, unexplained hypokalaemia, osteoporosis, hypertension or diabetes at a young age → review all steroid routes first, then one first-line test per the local endocrine pathway. Rapidly progressive → Urgent
- Drugs: antipsychotics, lithium, valproate, mirtazapine, steroids, insulin, sulfonylureas, pioglitazone, pregabalin → review with the prescriber. Antipsychotic changes are psychiatry-led.
- Women: persistent bloating, early satiety or pelvic pain (especially 50+) → CA125 and USS per NG12. Consider pregnancy and PCOS.
- Ask: binge-eating, mood, alcohol, OSA symptoms, recent smoking cessation.
3Assess — targeted, not routine panels
☐ BMI (ethnicity-adjusted: obesity ≥27.5) ☐ Waist-to-height if BMI <35: ≥0.5 increased risk ☐ BP, pulse, JVP, oedema, thyroid, striae, acanthosis ☐ HbA1c, TSH, U&E, LFTs, lipids, urine ACR; albumin if oedema
Not: Cushing's tests for uncomplicated obesity; blaming hypothyroidism without biochemistry.
4Classify — only once block 1 is fat
- Lifestyle (commonest) — energy imbalance, sleep, alcohol, ultra-processed food → block 5.
- Drug-induced — gain follows a new medicine → medication review.
- Endocrine — hypothyroidism (modest, mainly fluid), Cushing's, PCOS; hypothalamic or insulinoma rare.
- Other — stopping smoking or stimulants; sarcopenic obesity (BMI looks stable).
- Uncertain — say so; do not label it "lifestyle" until drugs and fluid are excluded.
5Treat today
- Lifestyle: 500–600 kcal/day deficit, ≥150 min/week activity, behavioural support or Tier 2 programme; aim 5–10% loss.
- Medicines (NICE + local commissioning): tirzepatide (TA1026) or semaglutide 2.4 mg in a specialist service (TA875) → consider stopping if <5% lost at 6 months. Orlistat: continue beyond 3 months only if ≥5% lost.
- Tirzepatide: non-oral or barrier contraception for 4 weeks after starting and each dose step. Stop semaglutide 2 months, tirzepatide 1 month before planned pregnancy. Doses: NICE/SPC, BNF, local formulary.
- Antipsychotics: metabolic checks at baseline, 12 weeks, 1 year, then annually; do not switch from primary care.
6Refer routinely
- Specialist weight / bariatric: BMI ≥40, or 35–39.9 with a significant comorbidity (lower for some ethnic groups). Recent-onset T2DM: expedited at ≥35. Do not delay with repeated lifestyle attempts.
- Endocrinology: abnormal Cushing's test; PCOS with severe hyperandrogenism or uncertainty.
- Hepatology: advanced fibrosis or cirrhosis on the local pathway — not FIB-4 alone. Severe OSA → CPAP assessment.
7Never reassure by
- "Lifestyle" before drugs and fluid are excluded.
- Leg or abdominal swelling put down to fat.
- BMI alone — oedema, muscle and older age mislead.
- "Lack of willpower" — the drivers are complex.
- White striae of obesity mistaken for violaceous Cushing's striae, or vice versa.
- Repeated lifestyle attempts when referral criteria are met.
8Safety-net — say it, then document it
999 “Breathless at rest or cannot lie flat, pink frothy spit, very drowsy, confused or very cold.” Same day “Swelling of the legs or tummy getting quickly worse, much less urine, or frothy urine with swelling. On a weight-loss injection: severe tummy pain that does not settle (stop it, A&E); sudden loss of vision in one eye (eye casualty or A&E); vomiting so you cannot keep fluids down.”
Within 2 weeks “Tummy bloated or swollen most days, feeling full quickly, new purple stretch marks, easy bruising or weak thigh muscles.” Remote or OOH: breathlessness, new swelling or drowsiness → same-day face to face (999 if breathless at rest).
✓Safe to leave primary care only if — all five, documented
Fat vs fluid decided: oedema, JVP, ascites checked
Medicines and steroid routes reviewed
TSH ± targeted tests; Cushing's only if features
BP, HbA1c, lipids, BMI recorded; eligibility checked
Safety-net, contraception advice and review date set
Summary of the full Reasoning GP weight gain algorithm, which holds the detail, examination, metabolic thresholds, drug safety and evidence. Sources: NICE NG246, TA1026, TA875, NG106, NG12 (updated April 2026), NG145, CG178, NG49; NHS England and local pathways; MHRA. Clinical reference — follow local pathways and check doses: NICE/SPC, BNF.